Abstract:

The microscopic local environmental structure of Cu2+ ions in copper chloride solutions was investigated by X-ray absorption fine structure (EXAFS) spectroscopy. The effects of salt concentration and freeze-thaw (FT) treatment on the first coordination shell of Cu2+ were analyzed by examining the Cu K edge EXAFS spectra of CuCl2 aqueous solutions before and after FT treatment at various concentrations. The EXAFS results show that Cu2+ has 3.0-4.3 oxygen nearest neighbors with Cu—O bond length of 0.192 -0.198 nm in the first coordination shell. These structural properties can be ascribed to the Jahn-Teller effect. We found differences in the microscopic local structure of Cu2+ for various concentrations in CuCl2 aqueous solutions.With an increase in the salt concentration, the coordination number of Cu2+ decreases and the Cu—O bond length increases in the first coordination shell. The influence of FT treatment on the microscopic local environmental structure of Cu2+ was determined fromthe fitting results of the structural parameters. The coordination number of Cu2+ in its first coordination shell and the degree of thermal disorder increase when the FT treatment is operated in CuCl2 aqueous solutions.

Key words: EXAFS, CuCl2 aqueous solution, Structure of hydrated ion, Coordination number, Concentration, Freeze-thaw treatment